Phase modulation



March 26, 1940. s. L. USSELMAN PHASE MODULATION kzm ma .536 E F ile'd June 25, 1937 INVENTOR" G.L.U$ LMAN BY 7%? ATTORNEY Patented Mar. 26, 1940 UNITED STATES PHASE MODULATION George L. Usselman, Port Jefferson, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Application June 25, 1937, Serial No. 150,269

11 Claims.

This application concerns a new and improved means for producing phase modulated oscillations. More specifically, this invention concerns a crystal controlled oscillator with means for phase modulating the oscillations produced by varying an impedance or reactance that is connected between an electrode of the frequency determining crystal and a controlling gridin a tube producing the oscillations.

Heretofore, phase modulations produced in a single tube crystal controlled oscillator using undivided excitation energy has been accompanied by undesired coincident amplitude modulation. In some cases the phase modulation produced in 15 a single tube crystal controlled oscillator is not sufliciently .linear. These defects are largely overcome in the present invention where in a single tube is connected in a novel circuit arrangement for producing oscillatory energy,

phase modulating the same, and supplying the same to an output circuit.

In describing my invention reference will be made to the attached drawing wherein the single figure illustrates the principles of my invention.

In the figure a multi-clectrode tube V of any type having a plurality of grid-like electrodes numbered 1 to 5 inclusive, has its anode A connected with an output circuit C1L1. Grids #l and #3 are connected as shown in a series circuit including a piezo-electric crystal PC, inductive reactance L, and capacitive reactance C. Either L or C may be variable at signal frequency. Biasing potentials are supplied to the electrodes 1 and 3 by resistors R1R2 connected as shown to a source of potential 132 which also supplies the potential for anode A. The potential supplied to grid 3 relative to the cathode is positive and grid 3 is in the oscillation circuit operating as an anode. The oscillation circuit is coupled to the output circuit C1L1 by the electron stream only of the tube. The remaining grid-like electrodes in the tube are for screening purposes or shielding purposes and may be connected as shown, #5 being connected to the cathode K and #2 and 45 #4 being connected to a point on source B2. Tubes having fewer electrodes may be used in place of the tube shown. The reactance C has one electrode connected by an insulating member D to the driven element S of an electro-dy- 0 namic driving unit MU having a field winding connected with a direct current field source not shown. The driven element S may be connected to the secondary of a transformer T, the primary of which is connected with any source of con- 55 trolling potentials A. F.

In operation we will assume that the crystal oscillator PC is oscillating normally and delivering carrier energy produced in the oscillatory circuit PC, L, and C to the output circuit C1141 by way of the electron stream in the tube V. Now, in accordance with my invention inductance L and condenser C are selected at such a value as to give the best results. These values can vary through a wide range and still satisfy the conditions necessary to the production of oscillatory energy, the phase of which is controlled in accordance with signals. The values of L and C depend in part on the frequency of PC, the degree of modulation desired, the desired amplitude of the oscillatory energy, etc. Briefly, for best operation the reactances of inductance L and condenser C are substantially equal-to each other when no modulating potentials are applied by T to S. This being the case, the reactances L and C will substantially balance out or, in other words, cancel, so that there is no phase shift in the crystal excitation energy delivered to the #l grid. In other words, if L and C are equal, being reactances of opposite sign, the lag which one tends to introduce in the oscillatory energy flowing in the series circuit is offset or neutralized or compensated by the lead which the other tends to introduce in the oscillatory energy flowing in said circuit. When signalling potentials or oscillations are supplied from A. F. to T and from T to the driven element S of the magnetic unit MU then movement is transmitted to the variable condenser C or condenser type microphone C through. the insulating link 0; rod D. Magnetic unit MU is a motor unit or driving unit similar to that used in a loudspeaker. Now, when the capacity of condenser C is changed this changes the balance between the inductance reactance and capacitive reactance so that the excitation from the crystal PC must reach the #l grid of tube V over a reactive network and its phase will consequently be shifted in a direction depending upon whether the network is unbalanced on the inductive side or on the capacitive side. If the network LC impedance is broadly capacitive the phase of the excitation voltage reaching grid #I will be advanced and if the network impedance is broadly inductive then the phase of the excitation voltage reaching the #l grid will be retarded. Consequently, the varying of capacity of condenser C relative to a mean value, diat is, on each side of a mean value at which C just offsets the effect of L, will cause a variation in the phase of the excitation voltage supplied to grid in both the leading and lagging directions. Consequently, the phase of the oscillatory energy produced in the circuit L, C, PC varies in accordance with the controlling potentials from the A. F.

The variation in the amplitude of the excitation energy supplied from PC to the #l grid may be kept very small because a large change in phase angle is obtained by this novel reactance arrangement, as the result of a small change of impedance therein. The grid bias resistor R6 is a part of the phase shifting network. This must be taken into account with calibrating the phase shift desired.

Condenser C may be any type of condenser or condenser type microphone or a crystal type microphone which changes its capacitive reactance when mounted mechanically or electrically. Some condenser type microphones are not exactly linear and this characteristic may be corrected to some extent by purposely adjusting the reactance of L and C so that they do not quite cancel, giving the phase of the excitation voltage impressed on the grid electrodes a slight bias which will correct the non-linearity of the microphone or condenser C.

It may also be desirable to connect a resistive element R; as shown in series with inductance L and condenser C to broaden the sharp tuning of these reactances in order to cut down the rapid phase shift at signal frequency near the point of mutual reactance cancellation. The output circuit C1L1 may be replaced by a resistance or impedance. When C1L1 is reactive as shown it may be tuned to the fundamental frequency, that is, the mean frequency of the oscillations produced by PC, L and C, or the output circuit C1L1 may be tuned to a harmonic of this fundamental fre-- quency.

An advantage of this invention is the provision of a balanced type phase modulator-which does not use or need to use phase splitting of the carrier energy in any part of the circuit. Moreover, the novel means or phase modulation principle of the present invention may be applied to relaying or amplifying circuits by merely inserting the phase modulating means L, C, T, M. U., D in a circuit between any two stages in a transmitter.

I claim:

1. In a phase modulation system, a circuit comprising inductive and capacitive reactance in series, means for causing wave energy, to be phase modulated, to flow in said series circuit, said inductive and capacitive reactances having substantially equal mean reactive values at the frequency of said wave energy flowing therein, means for varying the mean value of one of said reactances in accordance with signals to vary the combined characteristic of said reactances and thereby vary the phase of the wave energy flowing in said series circuit in accordance with signals, and means coupled with said series circuit for utilizing said phase varied wave energy.

2. An arrangement as recited in claim 1 wherein said series circuit includes frequency stabilizing means in series with said reactances.

3. In a'phase modulation system, an electron discharge tube having a cathode and a plurality of additional electrodes one of which serves as an anode, means including series reactances of opposite sign and substantially equivalent mean reactive value connecting electrodes of said tube in a series circuit in which wave energy to be phase modulated is caused to flow, means for varying the value of one of said reactances of said series circuit about its mean value at signal frequency to thereby control the combined character of said reactances and consequently the phase of said wave energy on one of said electrodes, and means connecting said electrode which serves as an anode in an output circuit coupled to said electrodes connected in said series circuit substantially by the electron stream of the tube only.

4. In a phase modulation system, an electron discharge tube having a cathode and a plurality of additional electrodes one of which serves as an anode, means including series reactances of opposite sign and substantially equivalent mean reactive value connecting a pair of said additional electrodes in an oscillation generating circuit in which oscillations flow in said reactances in series between said electrodes, means for varying the value of one of said reactances about its mean value at signal frequency to thereby control the combined character of the series reactances and consequently the phase of the oscillations reaching one of said electrodes at signal frequency, and an output circuit connected with said electrode which serves as an anode.

5. In a phase modulation system, an electron discharge tube having an anode, a cathode, and a plurality of grid-like electrodes one of which serves as an anode, an output circuit connected with said anode, means including series reactances of opposite sign and substantially equivalent mean value connecting said grid-like electrode serving as an anode to another of said gridlike electrodes to form an oscillation generating circuit in which oscillatory energy flows between said electrodes, said oscillation generating circuit being coupled to said output circuit by the electron stream only of the tube, and means for.

varying the value of one of said reactances about its mean value at signal frequency to thereby control the combined characteristic of the series reactances and consequently the phase of the oscillations reaching one of said grid-like electrodes at signal frequency to thereby vary the phase of the oscillatory energy supplied to said output circuit.

6. A system as recited in claim 1 wherein said one of said reactances, the mean value of which is varied, is the capacitive reactance.

7. A system as recited in claim 3 wherein said one of said reactances, the value of which is varied about its mean value, is capacitive.

8 In a system for phase modulating wave energy, an electron discharge device having a cathode, an output electrode, and a. plurality'of auxiliary electrodes, a circuit including frequency stabilizing means and series inductive and capacitive reactances connected between two of said auxiliary electrodes to comprise an oscillation generating means in which alternating current is caused to flow when the electrodes of said device are energized, an output circuit in which alternating current is caused to flow connected with saidoutput electrode, said output circuit being coupled to the first circuit by the electron stream only of said device, and means for varying the value of one of said reactances in accordance with signals for modulating the phase of the alternating current flowing in said output circuit.

9. A system as recited in claim 3 wherein said output circuit is tuned to a harmonic of said wave energy.

10. A system as recited in claim 8 wherein said output circuit is tuned to a harmonic of the frequency of the alternating current flowing in said first named circuit.

caused to flow when the electrodes 01' said device are properly energized, an output circuit in which alternating current voltages are produced,

connected with said output electrode and cathode, said output circuit being coupled to the first circuit substantially by the electron stream only of said device, and means for varying the value of one of said reactances in accordance with signals for modulating the phase of the alternating current voltages produced in said 10 output circuit.

GEORGE L. USSELMAN. 

